Processing of visual information begins when quanta of light are absorbed by the photopigments of the rods and cones. Tremendous advances in our understanding of the structure and function of the retina and visual pathways have occured in the recent past. However, one area of investigation - the quantification and specification of the spatial distribution of rods and cones - has been grossly neglected. There is only one study (Osterberg, 1935) that systematically investigated the distribution of rods and cones in the human retina, and he described only one retina! The basic aim of the proposed research is to quantitatively describe and characterize the receptor mosaic of the adult human and rhesus retina, and to provide the data in a form that will be readily usable by the anatomists; electrophysiologists, psychophysicists, and clinicians doing visual research or evaluation in these two species. Our basic technique will be to analyze the receptor mosaic using flat whole mounts of unstained retinas and interference contrast microscopy. We will cross validate our results with tangential sections of plastic imbedded material. We will also apply scanning electron microscopy (SEM) to the analysis of the receptor mosaic. Shrinkage and deformation of the tissue will be carefully analyzed. Quantification of the receptor mosaic with an image analyzing computer will make extensive analysis of a number of retinas feasible. In addition we will: (1) describe the mosaic as a function of developmental age, (2) apply sophisticated mathematical techniques to characterize the spatial patterning and distribution of the rods and cones, and (3) attempt to analyze the mosaic using SEM viewing of retinas mounted on a sphere-a condition that more closely resembles the living eye. Our results will provide the fundamental mosaic description necessary for further advances in our understanding of image processing in the primate retina.